Resistance developed by mosquitoes to available chemical insecticides and restrictions on their use favor the development of host-specific microbial agents for operational mosquito control. The proposed research continues investigation of fermentation production, storage, activation and application of the sexual stage (oospores) of Lagenidium giganteum. This is the only eukaryotic biological control agent of medically important arthropods with immediate potential for use in operational control programs. Conventional approaches to yield optimization using stirred tank fermentation will focus on alteration will focus on alteration of culture parameters at specific developmental stages of the fungus. Response surface analysis will be used to accelerate the development of optimum oospore yields. Modification of fermentation conditions to optimize synthesis of specific compounds associated with oosporogenesis will be attempted. Storage and activation protocols will be modified to limit premature abortion of converted oospores. Multi- hectare field tests will continue, including in areas in which mosquito- borne disease is a severe health problem. This sterol auxotrophic fungus requires an exogenous source of sterols to enter its reproductive cycle. Precise structural requirements for bulk and regulatory roles of sterols will be determined. Phospholipids, including sphingolipids which regulate enzymic activity, are involved in the control of L. giganteum growth and morphogenesis. The effect of sterols on phospholipid uptake, synthesis and metabolism will be examined. Sterol regulation of eicosanoid and related oxygenated fatty acid metabolism will be investigated and correlated with specific developmental stages of the fungus. Eicosanoids are mediators of the inflammatory response in mammals. Use of this fungus as a model system will provide the background for increasing oospore yields for commercial fermentation production of L. giganteum, and for future investigations of lipid-mediated enzymic activity.